Evidence of correlation between electronic density and surface acidity of sulfated TiO2

Correlation between the electronic structure and surface acidity of TiO2-SO 42- with different SO42- amounts has been investigated by means of NH3-TPD, NH3-FT-IR and XPS. With the increase of sulfate loadings, the shift of bin ding energies of O 1s in hydroxyl and Ti 2p(2/3) increases and is proportio nal to total acidity. A linear relation is obtained between Ti 2p binding e nergy shift and Lewis acid sites, while the shift in O 1s binding energy is attributed both to the generation of NH3 hydrogen bond and of Bronsted aci d sites. Accordingly, the results obtained from XPS measurements provide ev idence that the ammonia adsorption sites are attributed to the decrease of electron density of O 1s in hydroxyl (Bronsted type and H bonded) and Ti 2p (2/3) (Lewis type) by inductive effect of the neighboring sulfate ion.